Process for producing phosphor and plasma display panel unit

ABSTRACT

Fine particles of a phosphor are weighed, mixed, and filled. Provided after this step are at least one step of firing the particles in a reducing atmosphere, and a step of pulverizing, dispersing, rinsing, drying and then performing oxygen ion implantation treatment for implanting oxygen ions and annealing the particles, after the step of treatment in the reducing atmosphere. This method recovers oxygen vacancy in the host crystal of the phosphor.

TECNICAL FIELD

The present invention relates to a plasma display panel device and amethod of fabricating phosphors therefor. Especially, the phosphors canpreferably be used for image display devices represented by a plasmadisplay device, and illuminators represented by a rare-gas dischargelamp and a high-load fluorescent lamp.

BACKGROUND ART

Among color display devices used for image display on a computer ortelevision screen, a plasma display panel device has recently beendrawing attention, as a large and thin color display device having lightweight.

A plasma display device performs additive color mixing of three primarycolors (red, green, and blue) to provide full-color display. For thefull-color display, a plasma display device has phosphor layers foremitting the respective three primary colors, i.e. red, green, and blue.In discharge cells of a plasma display device, discharge of a rare gasgenerates ultraviolet light having a wavelength up to 200 nm. Theultraviolet light excites phosphors of respective colors to generatevisible light of respective colors.

Known as phosphors of the respective colors are (Y, Gd) BO₃:Eu³⁺ andY₂O₃:Eu³⁺ for red emission, (Ba, Sr, Mg)O.aAl₂O₃:Mn²⁺ and Zn₂SiO₄:Mn²⁺for green emission, and BaMgAl₁₀O₁₇:Eu²⁺ for blue emission, for example.

Among these, for a blue phosphor called BAM that contains BaMgAl₁₀O₁₇ asits base material, Eu, i.e. its center of emission, must be activateddivalent, in order to improve emission luminance. Thus, this phosphor isfabricated by firing in a reducing atmosphere (see “Phosphor Handbook”,Phosphor Research Society, Ohmsha, pp.170, for example.) This isbecause, if the phosphor is fired in an oxidizing atmosphere, Eu isactivated trivalent and Eu cannot substitutes for the bivalent Baposition properly in its host crystal. For this reason, Eu cannot be anactive emission center, and this deteriorates emission luminance.Further, Eu does not accomplish its original purpose, and generates redemission peculiar to Eu³⁺.

For a red phosphor, europium-activated yttrium oxysulfide (Y₂O₂S:Eu³⁺),because Eu must be activated trivalent, the phosphor is fabricated byfiring in an oxidizing atmosphere. Meanwhile, for a phosphor in whichits host crystal is made of an oxide, it is considered that oxygen atomsare deprived from the host crystal in firing and thus oxygen vacancy isgenerated in the phosphor. Disclosed as a method of recovering suchoxygen vacancy is firing the materials in an inert gas containing oxygento activate Eu trivalent and provide Y₂O₂S:Eu³⁺ (see Japanese PatentUnexamined Publication No.2000-290649).

However, in comparison with an oxide phosphor fabricated by firing in anoxidizing atmosphere, for an oxide phosphor fabricated by firing in areducing atmosphere, the reducing atmosphere tends to deprive oxygenfrom the host crystal and oxygen vacancy in the host crystal increases.Further, when an oxide phosphor that must be fired in a reducingatmosphere is fired in an oxidizing atmosphere, keeping the number ofvalences inherent in the activator is difficult.

In other words, when a phosphor having much oxygen vacancy in its hostcrystal is subjected to high-energy ultraviolet light (having awavelength of 147 nm) irradiated by a plasma display device and ionimpact caused by discharge, the phosphor is likely to degrade with time.This is because, in the sites having oxygen vacancy, the bond betweenatoms is weak, and application of high-energy ultraviolet light and ionimpact to the sites tends to disturb the crystal structure and make thesites amorphous. The amorphous sites mean deterioration of the hostcrystal. In a plasma display device, such deterioration leads toluminance degradation with time, color shift caused by chromaticitychange, and image burn.

When an oxide phosphor that must be fired in a reducing atmosphere isfired in an oxygen atmosphere for the purpose of recovery of oxygenvacancy, for a BAM phosphor, for example, Eu is activated to Eu³⁺ andthis causes considerable luminance degradation.

The present invention addresses these problems, and aims to provide amethod of fabricating a phosphor, and a plasma display panel using thephosphor. With the fabricating method, even for a phosphor in which itsemission center, Eu or Mn, must be activated bivalent, and its hostcrystal is made of an oxide, its oxygen vacancy can be recovered withoutdeterioration of emission luminance.

DISCLOSURE OF THE INVENTION

The present invention is a plasma display device in which a plurality ofdischarge cells having at least one color is disposed, phosphor layershaving a color corresponding to the respective discharge cells aredisposed, and the phosphor layers are excited by ultraviolet light toemit light. At least one phosphor layer among the phosphor layers ismade of a phosphor that has a composition formula of Ba_((1−x−y))Sr_(y)MgAl₁₀O₁₇:Eu_(x) and undergoes oxygen ion implantationtreatment for implanting oxygen ions.

The phosphor of such composition has a high emission luminance.Additionally, the oxygen ion implantation treatment can recover oxygenvacancy in the host crystal without decreasing the emission luminance,thus providing a plasma display device having inhibited luminancedegradation during actual operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing a method of fabricating a phosphor inaccordance with an exemplary embodiment of the present invention.

FIG. 2 is a sectional view of a treatment device for implanting oxygenions in accordance with the exemplary embodiment of the presentinvention.

FIG. 3 is a perspective view of an essential part of a plasma displaydevice in accordance with the exemplary embodiment of the presentinvention.

FIG. 4 is a graph showing a luminance degradation factor of the phosphorfor use in the plasma display device in accordance with the exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

An exemplary embodiment of the present invention is detailed hereinafterwith reference to the accompanying drawings.

FIG. 1 is a flowchart showing a method of fabricating a phosphor inaccordance with the exemplary embodiment of the present invention.Synthesis of an aluminate phosphor, Ba_((1−x−y))Sr_(y)MgAl₁₀O₁₇:Eu_(x),is taken as an example.

In step 1, a step of weighing fine particles, generally the followingcarbonates, oxides, and hydrates are used and weighed as the materialsof respective metals. In other words, barium compounds, e.g. bariumcarbonate, barium hydrate, barium oxide, and barium nitrate, are used asbarium materials. Strontium compounds, e.g. strontium carbonate,strontium hydrate, and strontium nitrate, are used as strontiummaterials. Magnesium compounds, e.g. magnesium carbonate, magnesiumhydrate, magnesium oxide, and magnesium nitrate, are used as magnesiummaterials. Aluminum compounds, e.g. aluminum oxide, aluminum hydrate,and aluminum nitrate, are used as aluminum materials. Europiumcompounds, e.g. europium oxide, europium carbonate, europium hydrate,and europium nitrate, are used as europium materials. These materialsare weighed out so as to have a predetermined molar ratio ofconstituting ions. Each material is not limited to carbonate, oxide, orhydrate, and can be any compound.

In step 2, a mixing step, a fluxing agent, i.e. a crystal growthaccelerator, such as aluminum fluoride, barium fluoride, and magnesiumfluoride, is mixed into the weighed materials, as required. In thisembodiment, a ball mill is used as a mixing means, for example, to mixthe materials for one to five hours. The materials can be mixed using aball mill by a wet method. However, instead of the mixing method using aball mill, a co-precipitation method, a method of mixing materials madeof alkoxide of respective metals in a liquid phase, or other methods canbe used.

In step 3, a filling step, such a mixture is filled into aheat-resistant crucible, such as a high-purity alumina crucible.

In step 4, a step of treatment in atmospheric air, the mixed powdersfilled in the crucible is fired in atmospheric air at temperaturesranging from 800 to 1,500° C. for one to 10 hours so that the growth ofthe host crystal is accelerated. Incidentally, because step 4 is foraccelerating the crystal growth, it is not an essential step.

In step 5, a step of treatment in a reducing atmosphere, the mixedpowders filled are fired in a reducing atmosphere, e.g. nitrogenatmosphere, at temperatures at which a desired crystal structure can beformed. The aluminate phosphor of the exemplary embodiment of thepresent invention is fired in the temperature range of 1,100 to 1,500°C., for one to 50 hours.

In step 6, a step of oxygen ion implantation treatment, after phosphorpowders of predetermined sizes are implanted with oxygen ions, they areannealed at temperatures ranging from 500 to 600° C., for approximatelyfive hours. Such oxygen ion implantation allows oxygen atoms to enterinto the oxygen vacancy of the host crystal generated during thetreatment in the reducing atmosphere, and thus the oxygen vacancy isrecovered.

In step 7, a step of pulverizing, dispersing, rinsing and drying thephosphor, after the mixed powders implanted with ions are sufficientlycooled, they are pulverized, dispersed, and rinsed by a wet method forone hour, using a bead mill, for example, as a dispersing means. Now,the mixed powders can be pulverized and dispersed using any dispersingdevice, e.g. a ball mill and jet mill, other than the bead mill.Thereafter, the phosphor powders pulverized, dispersed, and rinsed aredehydrated, and sufficiently dried; then sieved out to provide phosphorpowders.

In this embodiment, the step of treatment in a reducing atmosphere andthe following step of oxygen ion implantation treatment are performedonce each. However, the step of treatment in a reducing atmosphere toenhance luminance by activating Eu bivalent, and the step of oxygen ionimplantation treatment to recover oxygen vacancy in the host crystal canbe repeated a plurality of times. Additionally, one or more step oftreatment in atmospheric air to accelerate the growth of the hostcrystal can be provided before the step of treatment in a reducingatmosphere. After each treatment step, the powders can be pulverized,dispersed, and rinsed.

FIG. 2 is a sectional view of a treatment device for implanting oxygenions in accordance with the exemplary embodiment of the presentinvention. The temperature of vacuum chamber 41 can be controlled byheater 42 in the range of 400 to 700° C. After inlet valve 45 abovevacuum chamber 41 is opened, phosphor 40 having oxygen vacancy is fedfrom the top of vacuum chamber 41, and dropped by the small amount. Atthe middle of vacuum chamber 41, ion gun 44, an oxygen ion source, isprovided. Ion gun 44 structured to use a high-frequency power supply ispreferable. Oxygen gas is supplied from cylinder 49 through pipe 51. Theoxygen gas is ionized by plasma generated by a high-frequency powersupply (not shown). The ionized gas is accelerated at a predeterminedaccelerating voltage to provide oxygen ion beams. Then, phosphor 40having oxygen vacancy dropped is irradiated with an oxygen ion beam, andthus changed to phosphor 43 having oxygen vacancy recovered.

One oxygen ion beam can be radiated onto only the limited surfaces ofphosphor 40 having oxygen vacancy. For complete oxygen vacancy recovery,transfer pipe valve 46 is opened to allow phosphor 40 having oxygenvacancy to go upward through transfer pipe 48 and drop into vacuumchamber 41 again. This operation is repeated until the oxygen vacancy iscompletely recovered. After phosphor 40 having oxygen vacancy undergoesa predetermined oxygen vacancy recovery treatment, it is taken out byrelieving vacuum and opening exhaust valve 47.

Next, various kinds of aluminate phosphors,Ba_((1−x−y))Sr_(y)MgAl₁₀O₁₇:Eu_(x), are treated at least in a reducingatmosphere and then subjected to oxygen ion implantation. Thecharacteristics of respective aluminate phosphors are describedaccording to the examples.

EXAMPLE 1

Powders of sufficiently dry barium carbonate [BaCO₃], magnesiumcarbonate [MgCO₃], europium oxide [Eu₂O₃], and aluminum oxide [Al₂O₃]are prepared as the materials. These materials are weighed out so as tohave a molar ratio of constituting ions ofBa:Mg:Eu:Al=0.99:1.00:0.01:10.00. Next, after aluminum fluoride is addedto the weighed materials, as a crystal growth accelerator, the mixtureis mixed for three hours using a ball mill.

Next, the mixture is filled into a high-purity alumina crucible andfired in atmospheric air at a temperature of 1,200° C. for one hour.Then, the mixed powders fired are fired again in a reducing atmospherecontaining 20% of nitrogen gas and 80% of hydrogen gas, at 1,200° C. for10 hours. Sequentially, after the fired powders are pulverized,dispersed, rinsed, dried, and classified, they are repeatedly irradiatedwith oxygen ion beams several times using the device for implantingoxygen ions of FIG. 2. The amount of oxygen introduced from the ion gunis 10 cc/min. Thereafter, the temperature in the vacuum chamber is setto 500° C., and the powders are annealed for five hours.

Then, the powders that have undergone these treatments are rinsed. Therinsed mixed power phosphor is dehydrated, sufficiently dried, and thensieved out to provide phosphor powder having a general formula of Ba_(0.99) MgAl₁₀O₁₇:Eu_(0.01).

Next, the fabricated phosphor powder is irradiated with vacuumultraviolet light having a peak wavelength of 146 nm obtained by avacuum ultraviolet excimer laser irradiation equipment (146-nm lightirradiation equipment manufactured by Ushio Inc.), and the luminancewith respect to the irradiation time is measured using a luminance meter(LS-110 manufactured by Konika Minolta Japan). In this invention, as thecharacteristic value of luminance, a relative luminance value definedhereinafter is set to a performance index. The relative luminance valueis obtained by multiplying the relative initial luminance of eachphosphor by a luminance sustaining factor. Now, the relative initialluminance is defined as follows. When the initial luminance of aconventional phosphor is set to 100, the rate of the initial luminanceof each example is indicated by the relative initial luminance. Theluminance sustaining factor is a percentage obtained by dividing theluminance of the material of each example after 5,000 hours by itsinitial luminance. In other words, the relative luminance value is forcomparing the luminance of phosphors after a curtain period between theconventional phosphor and the phosphor of the example. The ratios ofconstituting materials, treatment conditions, and relative luminancevalues are shown in Table 1.

EXAMPLES 2 AND 3

Example 2 is made of the same materials as Example 1; however, it has amolar ratio of constituting ions of Ba:Mg:Eu:Al=0.9:1.0:0.1:10.0.Example 3 is also made of the same materials as Example 1; however, ithas a molar ratio of constituting ions of Ba:Mg:Eu:Al=0.8:1.0:0.2:10.0.The difference between Examples 2 and 3, and Example 1 is as follows.For Example 2, the mixture is fired in atmospheric air at 1,400° C. forone hour, and in a reducing atmosphere having a partial pressure ratioof N₂:H₂=95:5 at 1,100° C. for 10 hours. For Example 3, the mixture isfired in atmospheric air at 800° C. for one hour, and in a reducingatmosphere having a partial pressure ratio of 100% of N₂ at 1,200° C.for 10 hours. Then, phosphor powders fabricated under these conditionsare evaluated using the relative luminance values like Example 1. Table1 shows treatment conditions, relative luminance values, and otherresults.

EXAMPLES 4 THROUGH 9

For all these examples, powder of strontium carbonate [SrCO₃] is addedto the materials of Example 1. However, Example 4 has a molar ratio ofconstituting ions of Ba:Sr:Mg:Eu:Al=0.89:0.10:1.00:0.01:10.00. Example 5has a molar ratio of constituting ions ofBa:Sr:Mg:Eu:Al=0.8:0.1:1.0:0.1:10.0. Example 6 has a molar ratio ofconstituting ions of Ba:Sr:Mg:Eu:Al=0.7:0.1:1.0:0.2:10.0. Example 7 hasa molar ratio of constituting ions ofBa:Sr:Mg:Eu:Al=0.69:0.30:1.00:0.01:10.00. Example 8 has a molar ratio ofconstituting ions of Ba:Sr:Mg:Eu:Al=0.6:0.3:1.0:0.1:10.0. Example 9 hasa molar ratio of constituting ions ofBa:Sr:Mg:Eu:Al=0.5:0.3:1.0:0.2:10.0. The difference between Examples 4through 9 and Example 1 is as follows. Example 4 is not fired inatmospheric air, and fired in a reducing atmosphere having a partialpressure ratio of 100% of H₂ at 1,100° C. for 10 hours. Example 5 isfired in atmospheric air at 1,300 C. for one hour, and in a reducingatmosphere having a partial pressure ratio of N₂:H₂=99:1 at 1,200° C.for 10 hours. Example 6 is fired in atmospheric air at 1,400 C. for onehour, and in a reducing atmosphere having a partial pressure ratio ofN₂:H₂=90:10 at 1,400° C. for 10 hours. Example 7 is fired in atmosphericair at 1,300 C. for one hour, and in a reducing atmosphere having apartial pressure ratio of N₂:H₂=98:2 at 1,300° C. for 10 hours. Example8 is fired in atmospheric air at 1,000 C. for one hour, and in areducing atmosphere having a partial pressure ratio of N₂:H₂=90:10 at1,300° C. for 10 hours. Example 9 is fired in atmospheric air at 1,200C. for one hour, and in a reducing atmosphere having a partial pressureratio of N₂:H₂=50:50 at 1,300 C. for 10 hours. Then, phosphor powdersfabricated under these conditions are evaluated using the relativeluminance values like Example 1. Table 1 shows treatment conditions,relative luminance values, and other results. TABLE 1 Reducing Oxygenion Atmo- atmosphere implantation spheric Tempera- Amount of Molar ratioof air ture H₂ implantation Relative constituting ions Temper- concen-Annealing luminance Ba Sr Eu General formula ature tration temperaturevalue Example 1 0.99 0 0.01 Ba_(0.99)MgA₁₁₀O₁₇: 1200° C. 1200° C. 10cc/min 76 Eu_(0.01)  80% 500° C. Example 2 0.9 0 0.1 Ba_(0.9)MgAl₁₀O₁₇:1400 1100 94 Eu_(0.1)   5 Example 3 0.8 0 0.2 Ba_(0.8)MgAl₁₀O₁₇:  8001200 92 Eu_(0.2)   0 Example 4 0.89 0.1 0.01 Ba_(0.89)Sr_(0.1)MgAl₁₀O₁₇:— 1100 73 Eu_(0.01)  100 Example 5 0.8 0.1 0.1Ba_(0.8)Sr_(0.1)MgAl₁₀O₁₇: 1300 1200 89 Eu_(0.1)   1 Example 6 0.7 0.10.2 Ba_(0.7)Sr_(0.1)MgAl₁₀O₁₇: 1400 1400 94 Eu_(0.2)  10 Example 7 0.690.3 0.01 Ba_(0.69)Sr_(0.3)MgAl₁₀O₁₇: 1300 1300 77 Eu_(0.01)   2 Example8 0.6 0.3 0.1 Ba_(0.6)Sr_(0.3)MgAl₁₀O₁₇: 1000 1300 94 Eu_(0.1)  10Example 9 0.5 0.3 0.2 Ba_(0.5)Sr_(0.3)MgAl₁₀O₁₇: 1200 1300 77 Eu_(0.2) 50 Comparative 0.8 0.1 0.1 Ba_(0.8)Sr_(0.1)MgAl₁₀O₁₇: 1300 1200 — 69Example Eu_(0.1)   1

COMPARATIVE EXAMPLE

As a comparative example, a phosphor having the same molar ratio of theconstituting ions as Example 5 is fabricated by the conventionalfabricating method (conventional phosphor). The difference from Example5 is that comparative example has no step of oxygen ion implantationtreatment for oxygen vacancy recovery. The luminance sustaining factorof this sample is 69%, and thus the relative luminance value is 69.

As obvious from Table 1, the average relative luminance value ofaluminate phosphors of Ba_((1−x−y))Sr_(y)MgAl₁₀O₁₇:Eu_(x) is larger thanthe relative luminance value of the comparative example, theconventional phosphor, by 16, in the range of 0.01≦x≦0.2 and 0≦y≦0.3,and the emission luminance has increased. When the amount of Ba, Sr, andEu, i.e. x and y, in the aluminate phosphors ofBa_((1−x−y))Sr_(y)MgAl₁₀O₁₇:Eu_(x) are within the above range,remarkable effects are obtained. However, for the amount of Mg and Al,when they are within the composition range of approximately ±5% of theabove molar quantities (Mg=1, and Al=10), the effect of improvingemission efficiency has not changed.

In Examples 1 through 9, conditions for firing in reducing atmospheresand preceding conditions for firing in atmospheric air for fabricatingthe samples are varied. However, it is considered that not the influenceof these different conditions on the relative luminance values, but theexistence of oxygen ion implantation treatment leads to the differencein the relative luminance values. This is because a difference in therelative luminance value of 20 is observed especially between Example 5and the comparative example, in which the molar ratio of theconstituting ions is identical but the existence of oxygen ionimplantation treatment for oxygen vacancy recovery is different.Further, the effect of oxygen ion implantation treatment can be inferredfrom the following reasons.

Firstly, Eu is often used as an activator that can be bivalent andtrivalent. In the example of BAM, a blue phosphor, it is necessary thatbivalent Ba substitutes for bivalent Eu while the host crystal ofBa_((1−x))MgAl₁₀O₁₇ is grown from its materials, to produce a stableemission center Eu²+. For this purpose, as a conventional basic firingmethod, the materials are fired in an appropriate reducing atmosphere athigh temperatures ranging from 1,000 to 1,500° C., for at least fourhours.

Secondly, as to the recovery of the oxygen vacancy of the host crystalgenerated in the reducing atmosphere, the effect of recovering oxygenvacancy has been recognized when the phosphor is implanted with oxygenions and annealed at temperatures ranging from 500 to 600° C.

Incidentally, Sr need not be contained in the composition of thephosphor. However, if Sr is contained, Sr²⁺ having a smaller iondiameter substitutes for a part of Ba²⁺, and the lattice constant of thecrystal structure is slightly reduced. Thus, the emission color of theblue phosphor can be made more desirable color.

Next, FIG. 3 is a perspective view of an essential part of a plasmadisplay device in accordance with the exemplary embodiment of thepresent invention. In front panel 10, display electrodes 15, each madeof scan electrode 12 a and sustain electrode 12 b, and dielectric layer13 covering display electrodes 15 are formed on transparent andinsulating front substrate 11. Further on this dielectric layer 13,protective layer 14 is formed.

A predetermined number of display electrodes 15 are formed at a constantpitch on front substrate 11. Dielectric layer 13 is generally formed byprinting and firing low-melting glass because the dielectric layer isformed after formation of display electrodes 15 to securely cover thesedisplay electrodes 15. As the materials of the glass paste, alow-melting glass paste having the composition of so-called(PbO—SiO₂—B₂O₃—ZnO—BaO) glass, containing lead monoxide [PbO], siliconoxide [SiO₂], boron oxide [B₂O₃], zinc oxide [ZnO], and barium oxide[BaO], can be used. Using this glass paste and repeating screen-printingand firing, for example, can easily provide dielectric layer 13 having apredetermined thickness. The thickness may be set according to thethickness of display electrodes 15 and target electrostatic capacity orother factors. In this embodiment of the present invention, thethickness of dielectric layer 13 is approximately 40 μm. Additionally, aglass paste containing at least one of lead monoxide [PbO], bismuthoxide [Bi₂O₃], and phosphorus oxide [PO₄] as a major constituent can beused.

Protective layer 14 is provided so that plasma discharge does notsputter dielectric layer 13. Thus, the protective layer is required tobe a highly sputtering-resistant material. For this reason, magnesiumoxide [MgO] is often used.

On the other hand, on rear substrate 16 that is transparent andinsulating like the front substrate, data electrodes 17 for writingimage data are formed in the direction perpendicular to displayelectrodes 15 on front panel 10. After insulating layer 18 is formed onrear substrate 16 to cover these data electrodes 17, barrier rib 19 isformed in parallel with and substantially at the center of each dataelectrode 17. The areas sandwiched between barrier ribs 19, phosphorlayers 20 are formed to constitute rear panel 50. These phosphor layers20 are formed adjacent to phosphors emitting red (R), green (G), or blue(G) light. These phosphor layers constitute pixels.

Formed as data electrodes 17 are films having laminated structures, suchas a single-layer film made of silver, aluminum, or cupper having lowelectric resistance, a two-layer film made of chromium and cupper, and athree-layer film made of chromium, cupper, and chromium, using thin-filmforming techniques, such as printing and firing, or sputtering.Insulating layer 18 can be formed by the same materials and film-formingmethods as dielectric layer 13. Additionally, a glass paste containingat least one of lead monoxide [PbO], bismuth oxide [Bi₂O₃], andphosphorus oxide [PO₄] as a major constituent can be used. The phosphorsfabricated by the above methods and emitting R, G, or B light areapplied to the areas sandwiched between barrier ribs 19 by an inkjetmethod, for example, to form phosphor layers 20.

When front panel 10 and rear panel 50 are faced with each other,discharge space 30 surrounded by barrier ribs 19, protective layer 14 onfront substrate 11, and phosphor layers 20 on rear substrate 16 isformed. Then, when this discharge space 30 is filled with a mixed gas ofNe and Xe at a pressure of approximately 66.5 kPa, and alternatingvoltages ranging from several dozens to several hundred kilohertz areapplied across each scan electrode 12 a and corresponding sustainelectrode 12 b for discharge, phosphor layers 20 can be excited byultraviolet light generated when excited Xe atoms return to their groundstate. This excitation causes phosphor layers 20 to emit R, G, or Blight according to the materials applied thereto. For this reason, whenthe pixels at which data electrodes 17 emit light and colors of thelight are selected, necessary colors can be emitted at predeterminedpixel sections for color image display.

FIG. 4 is a graph showing luminance degradation factors of the phosphorsfor use in the plasma display device. Pulse voltages having an amplitudeof 180V and a frequency of 15 kHz are applied across display electrodes15. The variations of emission luminance with time are examined for thephosphor of Example 5 fabricated in accordance with the exemplaryembodiment of the present invention and the phosphor of the comparativeexample fabricated by the conventional method. The initial emissionluminance is set to 100% and the emission luminance after each lightingperiod is divided by the initial emission luminance to provide aluminance degradation factor. For the phosphor fabricated by theconventional method, the luminance degradation factor after 5,000 hoursdecreases to 72%. In contrast, for the phosphor fabricated in accordancewith this exemplary embodiment of the present invention, an emissionluminance of 86% is maintained. Even only in terms of the luminancedegradation factor, an improvement of 14% has obtained, and luminancedegradation has been inhibited. This is because the phosphor fabricatedin accordance with this exemplary embodiment is implanted with oxygenions after being fired in a reducing atmosphere, and thus has lessoxygen vacancy and a smaller part of anamorphous structure in itscrystal structure. As a result, even with irradiation of ultravioletlight or ion impact applied thereto, degradation of the crystalstructure and thus luminance degradation are smaller.

In the description of this exemplary embodiment of the presentinvention, Eu²+ is used as an activator in BAM phosphors. However, alsofor other phosphors using Eu²+ as an activator, such as CaMgSi₂O₆:Eu,and a green phosphor (Ba, Sr, Mg)O.aAl₂O₃:Mn in which Mn²+ is used as anactivator and its host crystal is made of an oxide, the oxygen ionimplantation has effects of increasing emission luminance and inhibitingluminance degradation.

The present invention provides a method of fabricating a phosphorcapable of recovering its oxygen vacancy without decreasing its emissionluminance, even in the case of a phosphor in which its emission center,Eu or Mn, must be activated bivalent and its host crystal is made of anoxide. Further, this fabricating method can provide a plasma displaydevice having higher emission luminance and lower luminance degradation.

INDUSTRIAL APPLICABILITY

The present invention can recover oxygen vacancy of a phosphor withoutdecreasing its emission luminance, even in the case of a phosphor inwhich its emission center, Eu or Mn, must be activated bivalent and itshost crystal is made of an oxide. The present invention is useful toimprove the performance of image display devices represented by a plasmadisplay device and illuminators represented by a rare-gas discharge lampand a high-load fluorescent lamp.

1. A plasma display device in which a plurality of discharge cellshaving at least one color is disposed, phosphor layers having a colorcorresponding to the respective discharge cells are disposed, and thephosphor layers are excited by ultraviolet light to emit light, whereinat least one phosphor layer among the phosphor layers is made of aphosphor that has a composition formula ofBa_((1−x−y))Sr_(y)MgAl₁₀O₁₇:Eu_(x) and undergoes oxygen ion implantationtreatment for implanting oxygen ions.
 2. The plasma display device ofclaim 1, wherein, in the composition formula ofBa_((1−x−y))Sr_(y)MgAl₁₀O₁₇:Eu_(x), 0.01≦x≦0.20 and 0≦y≦0.30.
 3. Amethod of fabricating a phosphor in which at least one of Eu and Mn isadded as an activator thereof and a multiple oxide containing at leastone of elements Ba, Ca, Sr, and Mg is a host crystal thereof, the methodcomprising: firing mixed materials of the phosphor in a reducingatmosphere at least once; and performing oxygen ion implantationtreatment for implanting oxygen ions after the step of treatment in thereducing atmosphere.
 4. The method of fabricating a phosphor of claim 3,wherein, a composition formula of the phosphor isBa_((1−x−y))Sr_(y)MgAl₁₀O₁₇:Eu_(x), where 0.01≦x≦0.20 and 0≦y≦0.30.